Technology Background
The present invention relates to a motor, and more particularly, to a brushless motor.
Discussion of the Related Art
A brushless motor is a motor without a brush and a commutator (or collecting ring). A brushless motor operates by changing the alternating frequency and the wave form of a current wave supplied to the coils of a rotor. Brushless motors are widely used by manufacturers in different sizes because of their high efficiency, low energy consumption, low noise, super long life, high reliability, servo controllability, stepless frequency conversion, speed regulating, low cost, and ease of use.
A brushless motor comprises a casing, a printed circuit board (PCB), a rotor and a stator. The stator includes an upper insulating bobbin, a stator core, a lower insulating bobbin, and a winding on the stator core defining a plurality of coils. The upper insulating bobbin and the lower insulating bobbin are installed respectively on the upper end face and the lower end face of the stator core. A lead wire winds the coil wound portion, which is formed by an upper slot insulation of the upper insulating bobbin, a tooth portion of the stator core and a lower slot insulation of the lower insulating bobbin. Thus, the wound lead wire forms a winding. The PCB is installed on the upper insulating bobbin and electrically connected to the winding.
However, the present inventors have identified a number of problems regarding existing brushless motors.
For example, when an insulation displacement connection terminal is used, a terminal fixing block on the upper insulating bobbin is located along the radial direction of the upper insulating bobbin and a terminal socket on the terminal fixing block is located along the circumference of the upper insulating bobbin so the puncture notch of the insulation displacement connection terminal is located along the radial direction of the upper insulating bobbin. As a result, when a lead wire is wound on the stator winding, the lead wire must be routed out along the radial direction of the upper insulating bobbin so the radial dimension of the stator is increased.
Further, a brushless motor may be a permanent magnet motor with fractional slot winding. This arrangement may reduce the slot area that is occupied by the insulating bobbin, thereby improving the actual slot filling factor of the stator winding, reducing the resistance of the winding, and improving the efficiency of the motor. However, the armature reaction of this arrangement includes higher harmonics, thereby increasing the iron loss of the motor. Moreover, a permanent motor with a fractional slot winding structure may be easily caused to have local magnetic saturation, thereby increasing of vibration and noise of the motor because of asymmetry of the magnetic circuit.